Haskell在遞歸元組函數中的困難

Question

我有一個小程序讀入文件並將數據處理爲自定義數據類型。讀取該文件包含像這樣的數據線：

cat 10 20 dog 
hamster 12 2 wombat 
monkey 1 9 zebra 
lion 30 60 rhino 
... 

我處理文件的程序是這樣的：

main :: IO() 
    main = do 
    contents <- readFile "myfile.xyz" 
    let process = clean contents 
    let f = processFile process 
    print f 

clean :: String -> [[String]] 
clean x = Prelude.map words $ lines x 

processFile :: [[String]] -> [(XyzData)] 
processFile [[a,b,c,d]] = [(XyzData a (read b :: Int) (read c :: Int) d)] 
processFile (x:xs) = processFile xs 

data XyzData = XyzData { animal1 :: String, 
         number1 :: Int, 
         number2 :: Int, 
         animal2 :: String 
         } deriving (Show) 

我的問題是與processFile功能。目前，該功能只捕獲文件的最後一行並將其打印到屏幕上。我很困惑如何用一個元組實現遞歸，而不是在這個函數中使用append和list。任何人都可以告訴我如何解決我的功能和/或更好的實現這個功能？該程序的打印輸出應爲：

[XyzData {animal1 = "cat", number1 = 10, number2 = 20, animal2 = "dog"}, 
[XyzData {animal1 = "hampster", number1 = 12, number2 = 2, animal2 = "wombat"}, 
[XyzData {animal1 = "monkey", number1 = 1, number2 = 9, animal2 = "zebra"}, 
[XyzData {animal1 = "lion", number1 = 30, number2 = 60, animal2 = "rhino"}] 

感謝您的時間。

Answer 1

你可能打算

processFile :: [[String]] -> [(XyzData)] 
processFile ([a,b,c,d]:xs) = (XyzData a (read b :: Int) (read c :: Int) d) : processFile xs 
processFile (x:xs) = processFile xs 
processFile [] = [] 

你的第一圖案[[a,b,c,d]]比賽只有一個元素，這與恰好四個元素的列表列出。